U.S. patent number 9,170,130 [Application Number 14/352,009] was granted by the patent office on 2015-10-27 for fiber-optic sensor device having a second fiber bragg grating unit to reflect light passing through a fiber optic sensor.
This patent grant is currently assigned to INDUSTRIAL COOPERATION FOUNDATION CHONBUK NATIONAL UNIVERSITY. The grantee listed for this patent is INDUSTRIAL COOPERATION FOUNDATION CHONBUK NATIONAL UNIVERSITY. Invention is credited to Sang Jin Choi, Jae Kyung Pan.
United States Patent |
9,170,130 |
Pan , et al. |
October 27, 2015 |
Fiber-optic sensor device having a second fiber bragg grating unit
to reflect light passing through a fiber optic sensor
Abstract
Provided is a fiber-optic sensor device. The fiber-optic sensor
device is capable of sensing a change in physical quantity by using
two fiber Bragg grating units arranged within an optical fiber and
a fiber-optic sensor unit arranged therebetween, thereby
implementing a low cost fiber-optic grating sensor having a simple
structure without requiring a reference FBG.
Inventors: |
Pan; Jae Kyung (Jeonju-si,
KR), Choi; Sang Jin (Gimje-si, KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
INDUSTRIAL COOPERATION FOUNDATION CHONBUK NATIONAL
UNIVERSITY |
Jeonju-si, Jeollabuk-do |
N/A |
KR |
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Assignee: |
INDUSTRIAL COOPERATION FOUNDATION
CHONBUK NATIONAL UNIVERSITY (Jeonju-Si, Jeollabuk-Do,
KR)
|
Family
ID: |
48698065 |
Appl.
No.: |
14/352,009 |
Filed: |
December 31, 2012 |
PCT
Filed: |
December 31, 2012 |
PCT No.: |
PCT/KR2012/011861 |
371(c)(1),(2),(4) Date: |
April 15, 2014 |
PCT
Pub. No.: |
WO2013/100742 |
PCT
Pub. Date: |
July 04, 2013 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
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US 20140299753 A1 |
Oct 9, 2014 |
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Foreign Application Priority Data
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|
|
|
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Dec 29, 2011 [KR] |
|
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10-2011-0146515 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01K
11/3206 (20130101); G01D 5/268 (20130101); G01D
5/35316 (20130101); G01D 5/35354 (20130101); G02B
6/0208 (20130101) |
Current International
Class: |
G01J
1/04 (20060101); G01D 5/353 (20060101); G01K
11/32 (20060101); G01D 5/26 (20060101); G02B
6/02 (20060101) |
Field of
Search: |
;250/227.14-227.23,214R,214.1,221 ;385/10,12,37 ;356/477-479 |
References Cited
[Referenced By]
U.S. Patent Documents
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6097487 |
August 2000 |
Kringlebotn et al. |
6680472 |
January 2004 |
Thingbo et al. |
|
Foreign Patent Documents
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|
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|
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2000-283846 |
|
Oct 2000 |
|
JP |
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2004-233070 |
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Aug 2004 |
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JP |
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2006-138757 |
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Jun 2006 |
|
JP |
|
Other References
International Search Report for International Application No.
PCT/KR2012/011861. cited by applicant.
|
Primary Examiner: Le; Que T
Attorney, Agent or Firm: LRK Patent Law Firm
Claims
The invention claimed is:
1. A fiber optic sensor device comprising: a light source for
generating light; an optical fiber into which the light generated
by the light source enters; a first fiber Bragg grating unit
arranged in the optical fiber to reflect some of the light
generated by the light source; a fiber optic sensor unit arranged
in the optical fiber to change intensity of the light passing
through the first fiber Bragg grating unit based on a specific
physical quantity; a second fiber Bragg grating unit arranged in
the optical fiber to reflect some of the light passing through the
fiber optic sensor unit; and a monitoring unit for sensing the
specific physical quantity changed by the fiber optic sensor unit
based on a ratio of intensity of light between a reflected light
reflected by the first fiber Bragg grating unit and a reflected
light reflected by the second fiber Bragg grating unit.
2. The device according to claim 1, wherein the monitoring unit
includes: a filter unit for selectively passing a first reflected
light reflected by the first fiber Bragg grating unit and a second
reflected light reflected by the second fiber Bragg grating unit;
an photoelectric conversion unit for converting the first reflected
light and the second reflected light passing through the filter
unit into a first electrical signal and a second electrical signal,
respectively; and a signal processing unit for calculating a ratio
of strength of light between the first reflected light and the
second reflected light using the first electrical signal and the
second electrical signal and sensing the specific physical quantity
changed by the fiber optic sensor unit based on the ratio of
strength of light.
3. The device according to claim 2, wherein the filter unit is a
variable Fabry-Perot (F-P) filter for selectively passing light of
a specific wavelength according to a bias voltage.
4. The device according to claim 2, wherein the photoelectric
conversion unit is a photo diode for converting light into an
electrical signal.
5. The device according to claim 1, wherein the first fiber Bragg
grating unit and the second fiber Bragg grating unit have different
Bragg reflection wavelength characteristics.
6. The device according to claim 1, wherein the fiber optic sensor
unit is an intensity-type fiber optic sensor for changing intensity
of incident light according to the specific physical quantity and
outputting the light.
7. The device according to claim 1, wherein the optical fiber
includes n fiber Bragg grating units (n is a natural number) and
n-1 fiber optic sensor units respectively arranged between the n
fiber Bragg grating units, and the monitoring unit senses the
specific physical quantity changed by the fiber optic sensor unit
arranged between two fiber Bragg grating units adjacent to each
other within the optical fiber based on the ratio of strength of
light between two reflected light reflected by the two adjacent
fiber Bragg grating units.
8. The device according to claim 7, further comprising a
wavelength-division multiplexer for splitting light entering from
the light source by wavelength and inputting the split light into m
optical fibers, wherein there is provided m optical fibers (m is a
natural number).
Description
TECHNICAL FIELD
The present invention relates to a fiber optic sensor device, and
more specifically, to a fiber optic sensor device for sensing a
physical quantity using a fiber Bragg grating.
BACKGROUND ART
An optical fiber grating widely used for optical communication and
fiber optic sensor devices is generally manufactured by the change
of a refractive index of a fiber optic core which is generated by
radiating strong ultraviolet rays on the optical fiber.
At this point, the optical fiber grating is classified as a short
period optical fiber grating and a long period optical fiber
grating according to the characteristic of the optical fiber, such
as a refractive index modulation period or the like, and studied
and used as a reflection and penetration filter or the like in
relation to the wavelength based on the characteristic.
In addition, a fiber Bragg grating induces periodic changes of the
refractive index of the optical core in the axial direction. The
optical fiber grating has a characteristic of reflecting only the
rays satisfying a Bragg condition and having a narrow line width
(generally, 0.1 to 1 nm) around a Bragg wavelength and passing rays
of the other wavelengths. If temperature of the fiber Bragg grating
is changed or a stress is applied to the fiber Bragg grating, the
Bragg wavelength also is changed. Accordingly, a variety of
fiber-optic grating sensors for measuring temperature, strain,
pressure or the like using the characteristic have been
developed.
However, since the fiber-optic grating sensor requires an expensive
reference fiber Bragg grating (FBG), it is expensive and has a
complex structure. Accordingly, development of a measure for
implementing a fiber-optic grating sensor of a low price and a
simple structure is required.
DISCLOSURE OF INVENTION
Technical Problem
Therefore, the present invention has been made in view of the above
problems, and it is an object of the present invention to provide a
fiber optic sensor device for sensing a change in physical quantity
by using two fiber Bragg grating units arranged within an optical
fiber and a fiber optic sensor unit arranged therebetween.
Technical Solution
To accomplish the above object, according to one aspect of the
present invention, there is provided a fiber optic sensor device
including: a light source for generating light; an optical fiber
into which the light generated by the light source enters; a first
fiber Bragg grating unit arranged in the optical fiber to reflect
some of the light generated by the light source; a fiber optic
sensor unit arranged in the optical fiber to change intensity of
the light passing through the first fiber Bragg grating unit based
on a specific physical quantity; a second fiber Bragg grating unit
arranged in the optical fiber to reflect some of the light passing
through the fiber optic sensor unit; and a monitoring unit for
sensing the specific physical quantity changed by the fiber optic
sensor unit based on a ratio of intensity of light between a
reflected light reflected by the first fiber Bragg grating unit and
a reflected light reflected by the second fiber Bragg grating
unit.
In addition, the monitoring unit may include: a filter unit for
selectively passing a first reflected light reflected by the first
fiber Bragg grating unit and a second reflected light reflected by
the second fiber Bragg grating unit; an photoelectric conversion
unit for converting the first reflected light and the second
reflected light passing through the filter unit into a first
electrical signal and a second electrical signal, respectively; and
a signal processing unit for calculating a ratio of strength of
light between the first reflected light and the second reflected
light using the first electrical signal and the second electrical
signal and sensing the specific physical quantity changed by the
fiber optic sensor unit based on the ratio of strength of
light.
In addition, the filter unit may be a variable Fabry-Perot (F-P)
filter for selectively passing light of a specific wavelength
according to a bias voltage.
In addition, the photoelectric conversion unit may be a photo diode
for converting light into an electrical signal.
In addition, the first fiber Bragg grating unit and the second
fiber Bragg grating unit may have different Bragg reflection
wavelength characteristics.
In addition, the fiber optic sensor unit may be an intensity-type
fiber optic sensor for changing intensity of incident light
according to the specific physical quantity and outputting the
light.
In addition, the optical fiber may include n fiber Bragg grating
units (n is a natural number) and n-1 fiber optic sensor units
respectively arranged between the n fiber Bragg grating units, and
the monitoring unit may sense the specific physical quantity
changed by the fiber optic sensor unit arranged between two fiber
Bragg grating units adjacent to each other within the optical fiber
based on the ratio of strength of light between two reflected light
reflected by the two adjacent fiber Bragg grating units.
In addition, there is provided m optical fibers (m is a natural
number), and the fiber optic sensor device may further include a
wavelength-division multiplexer for splitting light entering from
the light source by wavelength and inputting the split light into
the m optical fibers.
Advantageous Effects
According to various embodiments of the present invention, there is
provided a fiber optic sensor device capable of sensing a change in
physical quantity by using two fiber Bragg grating units arranged
within an optical fiber and a fiber optic sensor unit arranged
therebetween, and thus a low cost fiber optic grating sensor having
a simple structure can be implemented without requiring a reference
FBG.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view showing a fiber optic sensor device according to
an embodiment of the present invention.
FIG. 2 is a view showing a fiber optic sensor device including a
plurality of fiber Bragg gratings and a plurality of fiber optic
sensor units in a measurement unit according to an embodiment of
the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be hereafter described in further detail
with reference to the accompanying drawings.
FIG. 1 is a view showing a fiber optic sensor device 100 according
to an embodiment of the present invention. As shown in FIG. 1, the
fiber optic sensor device 100 includes a light source 110, a first
fiber Bragg grating unit 120, a second fiber Bragg grating unit
125, a fiber optic sensor unit 130 and a monitoring unit 140.
The light source 110 generates broadband light including all
reflective wavelength bands of all fiber Bragg gratings (FBG)
included in the fiber optic sensor device 100. In addition, the
light source 110 inputs the generated light into an optical fiber
115 through a circulator 150.
The light generated by the light source 110 enters into the optical
fiber 115. In addition, the first fiber Bragg grating unit 120, the
second fiber Bragg grating unit 125 and the fiber optic sensor unit
130 are arranged in the optical fiber 115.
The first fiber Bragg grating unit 120 is arranged in the optical
fiber 115 and reflects some of the light generated by the light
source 110. A first reflected light reflected by the first fiber
Bragg grating unit 120 enters into the monitoring unit 140 through
the circulator 150.
The fiber optic sensor unit 130 is arranged in the optical fiber
115 and changes intensity of light passing through the first fiber
Bragg grating unit based on a specific physical quantity.
Specifically, the fiber optic sensor unit 130 is an intensity-type
fiber optic sensor for changing intensity of incident light
according to the specific physical quantity and outputting the
light. Accordingly, if a specific physical quantity is applied to
the fiber optic sensor unit 130, the fiber optic sensor changes
intensity of the incident light and outputs the light.
Specifically, the fiber optic sensor unit 130 changes intensity of
incident light and outputs the light according to applied voltage,
current, temperature, pressure, strain, a rotation rate, sounds,
concentration of gas or the like.
The second fiber Bragg grating unit 125 (<<135) is arranged
in the optical fiber 115 and reflects some of the light passing
through the fiber optic sensor unit 130. In addition, a second
reflected light reflected by the second fiber Bragg grating unit
125 (<<135) passes through the fiber optic sensor unit 130
and the first fiber Bragg grating unit 120 again and enters into
the monitoring unit 140 through the circulator 150.
At this point, the first fiber Bragg grating unit 120 and the
second fiber Bragg grating unit 125 have different Bragg reflection
wavelength characteristics. Accordingly, the first reflected light
and the second reflected light respectively have a different
wavelength.
The monitoring unit 140 senses a specific physical quantity changed
or applied by the fiber optic sensor unit 130 based on the ratio of
strength of light between the first reflected light reflected by
the first fiber Bragg grating unit 120 and the second reflected
light reflected by the second fiber Bragg grating unit 125. As
shown in FIG. 1, the monitoring unit 140 includes a filter unit
142, a photoelectric conversion unit 144 and a signal processing
unit 146.
The filter unit 142 selectively passes the first reflected light
reflected by the first fiber Bragg grating unit 120 and the second
reflected light reflected by the second fiber Bragg grating unit
125. To this end, the filter unit 142 uses a variable Fabry-Perot
(F-P) filter for selectively passing light of a specific wavelength
according to a bias voltage. Accordingly, since the first reflected
light and the second reflected light respectively have a different
wavelength, the filter unit 142 may separately passes the first
reflected light and the second reflected light.
The photoelectric conversion unit 144 converts the first reflected
light and the second reflected light passing through the filter
unit 142 into a first electrical signal and a second electrical
signal, respectively. To this end, the photoelectric conversion
unit 144 uses a photo diode for converting light into an electrical
signal.
The signal processing unit 146 receives the first electrical signal
and the second electrical signal. Then, the signal processing unit
146 calculates a ratio of strength of light between the first
reflected light and the second reflected light using the first
electrical signal and the second electrical signal and senses a
specific physical quantity changed by the fiber optic sensor unit
130 based on the ratio of strength of light.
The fiber optic sensor device 100 of such a structure has a
self-referencing characteristic capable of measuring changes in the
output of the light source by using the ratio of light reflected by
the two fiber Bragg gratings although the light source changes
output over a short or long time period. Such a self-referencing
characteristic does not need an expensive reference fiber Bragg
grating and makes it possible to implement an optical
intensity-based fiber optic sensor device 100 of a comparatively
simple structure.
A process of sensing a changed physical quantity by the signal
processing unit 146 using a ratio of the first reflected light
reflected by the first fiber Bragg grating unit 120 to the second
reflected light reflected by the second fiber Bragg grating unit
125 will be described below.
As shown in FIG. 1, the first fiber Bragg grating unit 120 and the
second fiber Bragg grating unit 125 respectively have reflectance
R.sub.11 and R.sub.12 and have Bragg reflection wavelength
characteristics (a central wavelength and a full wavelength at half
maximum (FWHM)) meeting conditions of the fiber optic sensor device
100.
Describing the principle of operation, light coming out of the
light source 110 proceeds to port {circle around (1)} and port
{circle around (2)} through the optical circulator 150 and enters
into the optical fiber 115. The first reflected light of the
incident light corresponding to the Bragg reflection wavelength is
reflected by the first fiber Bragg grating unit 120, and light of
the other wavelengths passes through the first fiber Bragg grating
unit 120 and the fiber optic sensor unit 130 and arrives at the
second fiber Bragg grating unit 125. The second reflected light of
a wavelength corresponding to the Bragg reflection wavelength of
the second fiber Bragg grating unit 125 is reflected by the second
fiber Bragg grating unit 125 and enters into port {circle around
(3)} by the optical circulator 150 by way of the fiber optic sensor
unit 130. The second reflected light coming out of port {circle
around (3)} is split into a first reflected light reflected by the
first fiber Bragg grating unit 120 and a second reflected light
reflected by the second fiber Bragg grating unit 125 according to a
bias voltage input into the filter unit 142. In addition, the first
reflected light and the second reflected light are converted into a
first electrical signal and a second electrical signal by the
photoelectric conversion unit 144.
Since the monitoring unit 140 is within a short distance, loss of
the optical fiber between the light source 110 and the optical
circulator 150 and between the optical circulator 150 and the
filter unit 142 or the photoelectric conversion unit 144 is
ignored. Under such an assumption, optical power P.sub.11 of the
first reflected light reflected by the first fiber Bragg grating
unit 120 and entered into the photoelectric conversion unit 144 can
be expressed as shown in mathematical expression (1).
P.sub.11=P.sub.inK.sub.C1-2K.sub.fiber1.sup.2R.sub.11K.sub.C2-3K.sub-
.fp (1)
Here, P.sub.in denotes an input optical power, K.sub.c1-2 denotes a
loss generated when the light proceeds from port {circle around
(1)} to port {circle around (2)} of the optical circulator 150,
K.sub.fiber1 denotes a loss between port {circle around (2)} of the
optical circulator 150 and the first fiber Bragg grating unit 120,
R.sub.11 denotes reflectance of the first fiber Bragg grating unit
120, K.sub.c2-3 denotes a loss generated when the light proceeds
from port {circle around (2)} to port {circle around (3)} of the
optical circulator 150, and K.sub.fp denotes a loss of the variable
F-P filter unit 142.
In addition, under the same assumption, optical power P.sub.12 of
the second reflected light reflected by the second fiber Bragg
grating unit 125 and entered into the photoelectric conversion unit
144 can be expressed as shown in mathematical expression (2).
P.sub.12=P.sub.inK.sub.C1-2K.sub.fiber1.sup.2K.sub.fiber2.sup.2K.sub.FBG1-
1.sup.2R.sub.12K.sub.C2-3K.sub.fpH.sub.11.sup.2 (2)
Here, K.sub.fiber2 denotes a loss between the first fiber Bragg
grating unit 120 and the second fiber Bragg grating unit 125,
K.sub.FBG11 denotes a loss depending on a transfer spectrum of the
first fiber Bragg grating unit 120, R.sub.12 denotes reflectance of
the second fiber Bragg grating unit 125, and H.sub.11 denotes a
transfer function of the fiber optic sensor unit 130 S.sub.11.
Measurement parameter X.sub.11 can be defined as shown below using
mathematical expressions (1) and (2).
.times..times..times..times..beta. ##EQU00001##
Here, .beta..sub.11 is a calibration factor, which is the same as
(H.sub.11.sup.2=1)X.sub.11 when the optical fiber has no loss.
Since H.sub.11 can be obtained through X.sub.11, if the ratio of
intensity of light X.sub.11 is changed, a physical quantity can be
calculated from mathematical expression (3).
In addition, if it is assumed that bias voltage of the variable F-P
filter unit 142 which passes a wavelength corresponding to the
reflective wavelength of the first fiber Bragg grating unit 120 is
V.sub.fp11 and change of the bias voltage of the variable F-P
filter unit 142 is .DELTA.V.sub.11 when the reflective wavelength
of the first fiber Bragg grating unit 120 is changed due to change
of temperature, since the maximum output at all the bias voltages
V.sub.11=V.sub.fp11+.DELTA.V.sub.11 of the F-P filter unit 142 in
which the reflective wavelength of the first fiber Bragg grating
120 can be positioned is measured as P.sub.11, a change in the
reflective wavelength of the fiber Brag grating caused by the
change of temperature does not influence the result of
measurement.
Although the reflective wavelength of the fiber Brag grating is
changed as the intensity of incident light and the temperature are
changed, H.sub.11 according to mathematical expression (3) derived
from mathematical expressions (1) and (2) remains constant.
According to the principles described above, the fiber optic sensor
device 100 according to the embodiment may sense a change in
physical quantity generated by the fiber optic sensor unit 130. In
addition, since the fiber optic sensor device 100 is advantageous
in that an expensive reference fiber Bragg grating which is
required in a conventional wavelength-based fiber Bragg grating
sensor structure is not needed and the change in physical quantity
is measured regardless of a change in incident light, a change in
temperature or the like, cost can be saved when an interrogator is
implemented.
Hereinafter, a case of including a plurality of fiber Bragg
gratings and a plurality of fiber optic sensor units will be
described with reference to FIG. 2. FIG. 2 is a view showing a case
of a fiber optic sensor device including a plurality of fiber Bragg
gratings and a plurality of fiber optic sensor units in a
measurement unit 410 according to an embodiment of the present
invention. Compared with the fiber optic sensor device of FIG. 1,
the fiber optic sensor device 200 of FIG. 2 includes a plurality of
fiber Bragg gratings and a plurality of fiber optic sensor units in
the measurement unit 410, and it is confirmed that these are
multiplexed by a wavelength-division multiplexer 420 for each
optical fiber.
Specifically, as shown in FIG. 2, each optical fiber configures a
row and includes n fiber Bragg grating units and n-1 fiber optic
sensor units respectively arranged between the n fiber Bragg
grating units. Here, n is a natural number.
In addition, the monitoring unit 140 senses a specific physical
quantity changed by the fiber optic sensor unit arranged between
two adjacent fiber Bragg grating units based on a ratio of
intensity of light between two lights reflected by two fiber Bragg
grating units adjacent to each other in the optical fiber.
In addition, there is provided m optical fibers (m is a natural
number), and the wavelength-division multiplexer 420 splits light
entering from the light source 110 by the wavelength and inputs the
split light into m optical fibers. Here, the wavelength-division
multiplexer 420 determines the unit of splitting a wavelength
according to the reflective wavelength bands of all the fiber Bragg
gratings included in each optical fiber.
In addition, all the plurality of fiber Bragg gratings included in
the measurement unit 410 may have different Bragg reflective
characteristics.
As described above, the fiber optic sensor device 200 including a
plurality of fiber Bragg gratings and a plurality of optical fiber
measurement units may sense a wide range of change in physical
quantity.
In addition, the fiber optic sensor device 100 may be placed far
away since the monitoring unit 140 and the fiber optic sensor unit
130 are connected using the optical fiber 115, and since
measurement points separated but multiplexed by the
wavelength-division multiplexer in parallel may have a different
length, respectively, there is no restriction in the distance
between a monitoring point and a measurement point.
In addition, as shown in FIG. 2, an optical intensity-based fiber
optic sensor unit is positioned between two fiber Bragg gratings,
and a physical quantity generated by the optical intensity-based
fiber optic sensor unit may be known by obtaining a calibration
factor .beta.mn through Xmn measured as shown in mathematical
expression (3), and since m*(n-1) optical intensity-based fiber
optic sensor units can be arranged, measurement can be
simultaneously performed at several points.
In addition, since the structure of the optical intensity-based
fiber optic sensor unit positioned between two fiber Bragg gratings
is changed depending on a physical quantity desired to be measured,
a physical quantity desired by a user can be measured, and
sensitivity can be appropriately adjusted according to the
structure of the fiber optic sensor unit.
In addition, since the optical intensity-based fiber optic sensor
unit positioned between two fiber Bragg gratings is configured as a
part of an optical fiber, a measurement range can be adjusted as is
desired by a user without restriction in the length of a section
desired to be measured, from a point sensor to distributed
sensors.
While the present invention has been described with reference to
the particular illustrative embodiments, it is not to be restricted
by the embodiments but only by the appended claims. It is to be
appreciated that those skilled in the art can change or modify the
embodiments without departing from the scope and spirit of the
present invention.
INDUSTRIAL APPLICABILITY
The present invention is applicable to a fiber optic sensor device
industry as a sensor device for sensing a physical quantity using
fiber Bragg gratings.
* * * * *